A compact nanoimprint lithography (NIL) apparatus using the driving power of a servomotor has been newly developed. A bilayer resist method using hydrogen silsequioxane (HSQ) as a top layer and AZ photoresist as a bottom layer has been proposed to achieve high-aspect resist patterns on a nonflat surface for room-temperature nanoimprint lithography (RT-NIL). The etching rate ratio of HSQ to AZ photoresist was higher than 100 for O2 reactive ion etching (RIE), indicating that the HSQ top layer has sufficient etching tolerance. We have achieved the high-aspect nanostructure patterns of 100-nm-linewidth and 1-µm-height using the NIL apparatus developed here.

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Fluorinated diamond-like carbon (F-DLC) has recently been applied as an antisticking layer on nanoimprint molds for semipermanent use, replacing the self-assembled monolayer currently used. An SiO2/Si mold was successfully coated with an F-DLC thin layer by chemical vapor deposition (CVD). The measured water contact angle of the F-DLC surface was 103°, which is 30° higher than that of the DLC surface. This value indicates the adequacy of F-DLC as an antisticking layer. Moreover, an F-DLC film had a high hardness of 24 GPa, similar to that of a DLC film (26 GPa). AZ resist patterns of 150 nm linewidth and 350 nm pitch were successfully obtained by thermal nanoimprinting using an F-DLC-coated mold. Finally, after repeating the imprinting for more than 100 times, the initial water contact angle of 103° for the surface of the F-DLC-coated mold was maintained.

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Room-temperature nanoimprint lithography (RT-NIL) and nanocontact printing (RT-NCP) processes using hydrogen silsesquioxane (HSQ) are promising techniques for fabricating various nanostructure devices. We have evaluated the linewidth dependence of the HSQ imprinted depth and the baking-temperature dependence of HSQ replicated patterns after RT-NIL. We have also demonstrated an advanced bilayer resist process with HSQ as a top layer and AZ photoresist as a bottom layer; this process can be used to fabricate high-aspect resist patterns on a Si substrate for RT-NIL and RT-NCP. The etching-rate ratio of the AZ photoresist to HSQ exceeds 100 for O2 reactive-ion etching, which means the etching tolerance of the HSQ top layer is sufficient to enable its use as a mask. We have fabricated high-aspect nanostructure patterns with 100 nm linewidth and 1 μm height using RT-NIL and 150 nm linewidth and 1 μm height by using RT-NCP. Furthermore, we have successfully transferred Au electrode patterns from a mold onto HSQ resin by using the adhesion properties of HSQ.

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BackgroundRecent studies report that surfaces displaying micrometer- or nanometer-sized undulating structures exhibit antibacterial effects. In previous work, we described the use of an advanced nanofabrication technique to generate an artificial biomimetic Moth-eye film by coating a polyethylene terephthalate (PET) film with nanoscale moth-eye protrusions made from a hydrophilic resin. This moth-eye film exhibited enhanced antibacterial effects in in vitro experiments. The aim of the present study was to verify the antibacterial efficacy of the Moth-eye film in practical environments.Materials and methodsThe antibacterial effects of three types of film (Moth-eye film, Flat film, and PET film) were compared. Sample films were pasted onto hand washing basins at the testing locations. After several hours, bacteria were collected from the surface of the sample films with one of three kinds of culture media stamper (to permit identification of bacterial species). The stampers were incubated for 48 hours at 35°C, and the numbers of colonies were counted.Results and discussionThe number of common bacteria including E. coli and S. aureus obtained from the Moth-eye film was significantly lower than those from the PET film (p<0.05) and Flat film at 1 hour (p<0.05). This study found that the Moth-eye film showed a long-term (6h) antibacterial effect and the Moth-eye structure (PET coated with nanoscale cone-shaped pillars) demonstrated a physical antibacterial effect from earlier time points. Therefore, the Moth-eye film appears to have potential general-purpose applications in practical environments.

We have newly developed an imprinting technique using liquid-phase hydrogen silsesquioxane (HSQ) as an alternate replication material for spin-coated HSQ resin currently used. Various patterns with linewidth ranging from 25 nm to 300 µm were demonstrated by imprinting using liquid-phase HSQ. We simultaneously fabricated arbitrary patterns including both submicron and greater than one hundred micron patterns by a one-step process. Moreover, after imprinting, the residual HSQ layer that remained in the compressed area was less than 10 nm thick.